The present invention relates to a nonaqueous electrolyte secondary battery.
In recent years, portable electronic appliances such as a camera-integrated VTR (video tape recorder), a mobile phone and a laptop personal computer have widely diffused, and it is strongly demanded to reduce their size and weight and to achieve their long life. Following this, batteries, in particular, light-weight secondary batteries capable of providing a high energy density have been developed as a power source.
Above all, a secondary battery utilizing intercalation and deintercalation of lithium (Li) for a charge and discharge reaction (so-called “lithium ion secondary battery”) is greatly expected because it is able to provide a higher energy density than a lead battery or a nickel-cadmium battery. Such a lithium ion secondary battery is provided with an electrolytic solution as well as a positive electrode and a negative electrode.
In order to enhance various performances of a nonaqueous electrolyte secondary battery, the development has been advanced extensively and intensively.
For example, it is reported in JP-A-2002-8718 and JP-A-2004-22336 that high-temperature characteristics and a cycle characteristics are improved by adding a sulfonic anhydride.
In JP-A-2002-8718, the battery life is studied in a system in which hydrogen fluoride is formed by the addition of water to an electrolytic solution containing a sulfonic anhydride.
Also, a lithium compound capable of generating a lithium ion is in general added to this electrolytic solution of a lithium ion secondary battery. Typical examples of the lithium compound include lithium hexafluorophosphate (LiPF6). However, many of such lithium compounds inclusive of lithium hexafluorophosphate react with water to form a fluorine ion (F−) (see, for example, JP-A-2002-216741). Then, it is said that the fluorine ion formed upon the reaction with water deteriorates the battery, thereby causing shortening of the battery life (see, for example, JP-A-2002-198088). JP-A-2002-198088 discloses that water is removed by disposing a carrier containing a scavenger substance capable of removing water within a system of the lithium secondary battery and releasing the scavenger substance from the carrier under a previously set up condition.
However, it has been noted that an acid anhydride containing a sulfonic group is instable and easily decomposable so that in existing electrolytic solutions, capabilities thereof are not sufficiently revealed. That is, in batteries of a system using a sulfonic anhydride, a further improvement in high-temperate storage properties is desired.